LEDs are becoming more widely used as light sources, and are attractive owing to their long lifetime and low power consumption. A number of LEDs—along with a driving circuit—can be incorporated in a “retrofit” light bulb to replace a less energy-efficient light source, for example an incandescent light bulb. An incandescent lamp can be driven directly from an AC mains voltage, for example 240 V. A halogen lamp is generally driven from a transformer which provides a constant DC input voltage, for example 12 V or 24 V. Conventional lamps can be dimmed using various techniques such as phase-cut dimming. For example, the incandescent lamp(s) of a lighting fixture can be dimmed by means of a phase-cut dimmer integrated into a wall-mounted switch for that lighting fixture. Similarly, a power supply for a halogen light source can incorporate a transformer as well as a dimmer.
There are various ways of ensuring that an LED retrofit lamp can be used with existing lighting fixtures. For example, an LED driver can be realised to convert a phase-cut mains AC input to corresponding DC signals for its LED load. However, such drivers can be very complex and can significantly add to the cost of the lamp.
Therefore, it is an object of the invention to provide an alternative way of dimming the LEDs of a lighting arrangement.